This invention relates generally to an improvement in a method of forming a large number of monocrystalline semiconductor regions in juxtaposition on an insulator substrate or film.
Silicon-on-sapphire (SOS) technology and silicon-in-insulator (SOI) technology have been known in the past as methods of forming monocrystalline semiconductor regions on the surface of an insulator. (Refer to the article on pages 573-578 of IEEE TRANSACTIONS ON ELECTRON DEVICES, Vol. ED-27, No. 3, Mar., 1980, and the article in IEEE ELECTRON DEVICE LETTERS, Vol. EDL-1, No. 10, Oct., 1980.) In SOS technology, a monocrystalline sapphire is employed as an insulator substrate, a polycrystalline or amorphous silicon layer is formed on this substrate, and this silicon layer is changed into a monocrystalline layer by laser annealing, for example. This technique is suitable for forming a high quality monocrystalline layer on an insulator, but has not yet been put to practical use because monocrystalline sapphire is expensive. On the other hand, in SOI technology amorphous quartz, glass or the like is employed as the insulator substrate, a polycrystalline or amorphous silicon layer is formed on this substrate, and the silicon layer changed into a monocrystalline layer by laser annealing, for example. This technique can eliminate the disadvantage of SOS technology, but has the new problem that cracks develop in the silicon layer after the laser annealing, because of the difference in the thermal expansion coefficients of the insulator substrate and the silicon layer.
In order to solve this problem, a method has been proposed in which the polycrystalline or amorphous silicon layer on the insulator substrate is divided into large number of island regions by grooves, and thereafter the silicon layer is changed into a monocrystalline layer. (Refer to the article in IEEE ELECTRON DEVICE LETTERS, Vol. EDL-1, No. 10, Oct., 1980.) In accordance with this method, however, the plane orientation of the crystals in the island regions which will become the monocrystal are non-uniform, and are generally (111) and (110). When semiconductor devices are formed in the island regions, therefore, the characteristics of the devices are non-uniform. More concretely, when MOSFETs are formed in the island regions, their threshold voltages, operating speeds and leakage currents are non-uniform; and when bipolar transistors are formed therein, their current amplification ratios h.sub.fe and leakage currents are non-uniform. Non-uniformity of the device characteristics results in a drop in production yield when integrated circuits with a large number of island regions are produced.